The present invention relates to sense circuits and, more particularly, to a circuit for sensing when an input signal exceeds a predetermined amplitude for producing an output signal indicative thereof. Specifically, the present invention pertains to ring signal detection circuit for use with electronic telephone tone ringer circuits to sense when a ringing signal is present on the telephone line to enable the electronic telephone tone ringer circuit to produce a simulated ringing tone.
The functions of contemporary telephones are being replaced by use of integrated circuitry. One such function that is being replaced by a solid state circuit is the telephone bell ringer. For instance, the MC34012 is a solid state Telephone Tone Ringer Circuit manufactured by Motorola, Inc. using bipolar linear integrated injection logic (I2L) technology. The MC34012 replaces the bell ringer and its companion bulky transformer circuitry of conventional telephone while simulating the ringing of the bell in response to the AC bell ringing signal applied to the Tip and Ring inputs of the telephone.
The MC34012 Telephone Tone Ringer Circuit includes circuitry for rectifying the AC bell ringing signal appearing on the Tip and Ring terminals and sensing the amplitude of the ringing signal for enabling tone generation circuitry therein to produce a tone ringer output signal as is understood. The tone generation circuitry comprises an output buffer amplifier that drives a piezo sound element. The MC34012 is packaged in an 8 leaded dual-line plastic package assembly: a very economical package.
Although the prior art circuit functions quite well, there has been found a need for a more powerful telephone tone ringer circuit, i.e., one that can provide more drive to the piezo sound element to thereby increase the amplitude of the ringing tone. It is also desired, in order to maintain cost at a minimum, to use the small 8 leaded plastic package presently being used in the assembly of the MC34012. However, to modify the MC34012 in order to produce a more powerful output signal requires the existing buffer amplifier to be modified to have push-pull outputs to double the available output voltage supplied at the outputs of the circuit. However, push-pull outputs require an additional output pin and therefore the existing 8 leaded plastic package could otherwise not be utilized since the MC34012 already requires use of 8 leads. Therefore, modification of the existing telephone tone ringer circuit is required.
Hence, there exists a need for an improved telephone ringer integrated circuit which can produce a more powerful output tone signal while requiring a minimum number of outputs in order to minimize production cost.